This invention relates to an apparatus for producing rigid sand cores for use in metal casting. These rigid sand cores are produced from a molding mixture comprising a refractory granular material such as sand and a relatively small quantity of a hardenable binder.
Several different types of machines are presently available for producing rigid sand cores. These machines produce such rigid sand cores according to any one of a number of known processes. One of the primary differences between these known processes is the method used for setting or curing the molding mixture. The different curing methods are characterized by the different hardenable binders used in the molding mixture. Another difference between these known processes is determined by the desired form of the rigid sand core, that is, whether the sand core to be produced is solid or hollow. Hollow rigid sand cores are commonly known as shell sand cores.
Machines for producing shell sand cores for foundry purposes employ a molding mixture comprising sand mixed with a relatively small quantity of a thermo setting resin. The molding mixture is placed in a core or molding box of iron or other metal having internal contours corresponding with the internal contours of the article to be ultimately produced from the sand core. The core box is heated to a given temperature which is sufficient to cause a coating of the molding mixture to form and build up to a required thickness on the interior surface of the core box. This coating is partially set by the initial heat applied to the core box and the remaining molding mixture is then dumped from the core box by rotating the core box. The coating or shell formed by the molding mixture is then subjected to additional heat in order to complete the setting or curing process. The shell sand core is then removed from the core box and used as a mold for metal casting. Examples of this shell core process are shown and described in U.S. Pat. No. 3,511,302, issued to R. H. Barron on May 12, 1970, and U.S. Pat. No. 2,855,642, issued to G. W. Taylor on Oct. 14, 1958.
Another widely known method for producing rigid sand cores from a molding mixture of sand and a hardenable binder is known as the cold box process. In this process, the hardenable binder is a cold setting resin which reacts with a particular gas catalyst fed through to the core box to cure or set the molding mixture. Although many different gas mixtures may be employed as the catalyst, amine gas is often one of the primary constituents. After the molding mixture is hardened by the reaction with the cold setting catalyst, the gas catalyst is purged from the core box and the core is removed from the machine for use in metal casting. Examples of this cold box process are shown and described in U.S. Pat. No. 3,038,221, issued to F. Hansberg on June 12, 1962, and U.S. Pat. No. 3,702,316, issued to J. Robins on Nov. 7, 1972.
Many different modifications of these basic processes are known and used in the art. For example, solid sand cores also are formed by a process known as the hot box process which differs from the shell core process in that none of the molding mixture is dumped from the core box. Although the resins employed in the hot box process are usually different than the resins employed in the shell core process, the setting or curing of the molding mixture is accomplished by the application of heat to the core box. The core box is then removed from the machine and the solid sand core is utilized for metal casting. Various other processes, such as the warm box carbon dioxide process, are also known in the art.
Different machines are presently available in the art for producing rigid sand cores according to each one of the above known processes. Some of these known machines are capable of automatic operation. That is, one machine is known for automatically producing shell sand cores and another machine is known for producing cold box sand cores. Examples of such machines are the automatic shell core machine HS-16-RA, Redford Bulletin No. 704, and automatic cold box core machine CB-16-SA, Redford Bulletin No. 7201, produced by the Foundry Products Division of International Minerals and Chemical Corporation of Detroit, Michigan. In addition, some of these known machines have previously combined certain related sand core processes. For example, since the curing of the molding mixture in both the shell core process and the hot box process is accomplished by the application of heat, it is convenient to combine these two basic processes in the same machine. For example, automatic shell core machine HS-16-RA described above can also be used to automatically produce hot box sand cores. However, because of the many dissimilarities between the shell core process and the cold box process, no machine is presently known which can be conveniently programmed to automatically produce both cold box sand cores and shell sand cores.
Therefore, it is an object of this invention to provide a single machine for automatically producing both shell cores and cold box cores. This machine overcomes the practical difficulties previously encountered in combining such relatively different processes on the same machine. In addition, the combined sand core machine of the present invention is also capable of automatically producing hot box cores.
It is a further object of the present invention to provide an electric control circuit arrangement for automatically controlling the operation of the combined core machine during the hot box process, the cold box process or the shell core process. This circuit arrangement employs a unique combination of circuit elements, many of which perform different functions during each of the above different processes. Other circuit elements perform similar functions during each of the above different processes. In this manner, the number of circuit machine elements necessary for performing various functions in the above different processes is minimized and the operation of the machine is simplified. The control circuit arrangement is readily programmable for enabling the combined core machine to automatically produce sand cores according to each of the above processes.